In recent years, correction-type ribbons have gained increasing use in the typewriter field, use of such ribbons replacing to a large degree the earlier corrective methods designed to eliminate a typewritten error from the page.
Prior to the development of adhesively eradicable transfer compositions, the typewriter ribbon comprised a pigment layer which was bonded more or less strongly to the paper when applied thereto by the type face of a typewriter. Correction was effected by erasure or by the application of opaque white layer to the printed letter thereby allowing the error to be overturned and correction made.
With the advent of adhesively eradicable or lift-off correction ribbons, the approach changed from one which involved coating the error to a simplified removal technique in which, after the typewritten error was made, the imprint was removed from the paper by applying an adhesive surface thereto. The imprint was formed by a composition containing a pigment, a film-forming resin binder and a modifier designed to facilitate transfer of the pigment composition from the ribbon, e.g. a polyethylene tape, to the paper and prevent premature bonding of the composition on the paper.
In U.S. Pat. No. 3,825,470, for example, the pigment layer was applied to the tape substrate in a solvent dispersion and contained, apart from the pigment or an insoluble organic coloring agent, a resin binder and one or more modifying agents which serve to harden the binder and embrittle the latter so that it has a predetermined frangibility reducing its adhesion to the substrate. If the transferred pattern was not removed from the paper, the transfer eventually became more or less permanent.
The modifying agent was preferably a mixture of mineral oil and fatty acid esters selected from the group which consists of the octyl esters of fatty acids, isopropylpalmitate, butyl-stearate and mixtures thereof.